Spectrum sensor and angle restriction filter

ABSTRACT

An angle restriction filter that allows light incident thereon in a predetermined range of incident angles to pass, includes: an optical path wall section formed from a plurality of light shield members laminated in layers including a common material, thereby forming an optical path in a lamination direction of the light shield members; and a light transmission section formed in a region surrounded by the optical path wall section.

BACKGROUND

The entire disclosure of Japanese Patent Application No. 2010-075007,filed Mar. 29, 2010 is expressly incorporated by reference herein.

1. Technical Field

The invention relates to spectrum sensors and angle restriction filters.

2. Related Art

Spectrum sensors are used in the medical, agricultural and environmentalfields for diagnosing and examining objects. For example, in the medicalfield, a pulse oximeter is used to measure the oxygen saturation ofblood, using light absorption of hemoglobin. Also, in the agriculturalfield, a saccharometer is used to measure the concentration of sugarcontent of fruits, using light absorption of sugar.

For example, Japanese Laid-open Patent Application JP-A-6-129908describes a spectroscopic imaging sensor that restricts incident anglesof light with an optical fiber that optically connects between adichroic filter and a photovoltaic converter device, thereby restrictingthe transmission wavelength band of light to the photovoltaic converterdevice.

However, the spectrum sensors of related art entail a problem in that itis difficult to reduce their size. Therefore, placement of numeroussensors in a desired location or permanent placement thereof isdifficult.

SUMMARY

In accordance with an advantage of some aspects of the invention,spectrum sensors and angle restriction filters can be reduced in size.

In accordance with an embodiment of the invention, an angle restrictionfilter includes an optical path wall section formed from a plurality oflight shield members laminated in layers including a common material,thereby forming an optical path in a lamination direction of the lightshield members, and a light transmission section formed in a regionsurrounded by the optical path wall section. The angle restrictionfilter restricts incident angles of light that passes through theoptical path. According to the embodiment, the optical path is formedthrough forming the light shield members in layers on a substrate, suchthat very fine patterns can be formed, and the angle restriction filterthus can be manufactured in a small size.

In accordance with an aspect of the embodiment, the common material maypreferably be a material having a lower reflectance than that ofaluminum, for example, tungsten, copper, titanium nitride,titanium-tungsten, titanium, tantalum, tantalum nitride, chrome ormolybdenum. In accordance with this aspect, as the light shield membersare formed from a material having a low light reflectance, light thathits the wall surface of the optical path while traveling through theoptical path can be reduced. Therefore, even a small-sized anglerestriction filter can make it harder for light with incident anglesexceeding a specified restriction angle range to pass through theoptical path.

In the embodiment described above, the optical path wall section and thelight transmission section may preferably be formed on a semiconductorsubstrate, and a plurality of metal layers may preferably be laminatedrespectively through dielectric layers in a region outside the opticalpath and the optical path wall section. As the plurality of metal layersforming wiring layers on a semiconductor circuit are formed outside theoptical path and the optical path wall section, it is possible tosuppress incidence of light reflected from the metal layers in theoptical path, which makes it harder for light with incident anglesexceeding a specified restriction angle range to pass through theoptical path.

In accordance with an aspect of the embodiment described above, thelight shield members may preferably be formed from a conductivematerial, and electrically connected to the plurality of metal layers.Accordingly, the light shield members and the plurality of metal layersare electrically connected to one another, such that the light shieldmembers can be used as a part of the electrical circuit.

In accordance with an aspect of the embodiment described above, theoptical path defines a wall surface that may preferably have an inclinedsection inclined with respect to a direction perpendicular to thesubstrate. As the wall surface of the optical path has the inclinedsection, light that may hit the wall surface of the optical pass whiletraveling through the optical path can be reduced, such that it ispossible to make it harder for light with incident angles exceeding aspecified restriction angle range to pass through the optical path.

In accordance with another embodiment of the invention, an anglerestriction filter includes an optical path wall section formed from aplurality of metal layers laminated in layers on a substrate, and lightshield members formed between the plurality of metal layers and having asmaller light reflectance than that of the metal layers, thereby formingan optical path in a lamination direction of the metal layers, and alight transmission section formed in a region surrounded by the opticalpath wall section. The angle restriction filter restricts incidentangles of light that passes through the optical path. According to anaspect of the embodiment, portions of the wall surface of the opticalpath which are formed by the light shield members are inclined withrespect to the direction of the optical path, respectively. Inaccordance with the embodiment, at least a portion of the wall surfaceof the optical path is inclined, such that light that may hit the wallsurface of the optical path while traveling through the optical path canbe reduced, and therefore it is possible to make it harder for lightwith incident angles exceeding a specified restricting angle range topass through the optical path.

In accordance with an aspect of the embodiment, the light shield membermay preferably be provided on its surface with a film formed from amaterial having a lower reflectance than that of aluminum, such as, forexample, titanium nitride, tungsten, copper, titanium-tungsten,titanium, tantalum, tantalum nitride, chrome or molybdenum. Inaccordance with this aspect, as the film having a low reflectance isformed on the surface of each of the light shield members, light thathits the wall surface of the optical path while traveling through theoptical path can be reduced, and therefore it is possible to make itharder for light with incident angles exceeding a specified restrictingangle range to pass through the optical path.

In accordance with another aspect of the embodiment described above, thewall surface of the optical path may preferably be formed with concaveand convex portions formed through changing a forming pattern of each ofthe light shield members at each of the layers. Accordingly, as the wallsurface of the optical path has the concave and convex portions, lightthat hits the wall surface of the optical path while traveling throughthe optical path can be reduced, and therefore it is possible to make itharder for light with incident angles exceeding a specified restrictingangle range to pass through the optical path.

In accordance with still another embodiment of the invention, a spectrumsensor includes the angle restriction filter set forth above, awavelength restriction filter that restricts wavelengths of light thatcan pass through the angle restriction filter, and a photodetectordevice that detects light that has passed through the angle restrictionfilter and the wavelength restriction filter. According to thisembodiment, the angle restriction filter described above is used, suchthat the spectrum sensor can be manufactured in a small size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views showing an angle restriction filterand a spectrum sensor in accordance with a first embodiment of theinvention.

FIGS. 2A-2E are views showing steps of forming the angle restrictionfilter.

FIG. 3 is a schematic view of an angle restriction filter in accordancewith a second embodiment.

FIG. 4 is a schematic view of an angle restriction filter in accordancewith a third embodiment.

FIG. 5 is a schematic view of an angle restriction filter in accordancewith a fourth embodiment.

FIG. 6 is a schematic view of an angle restriction filter in accordancewith a fifth embodiment.

FIG. 7 is a schematic view of an angle restriction filter in accordancewith a sixth embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred embodiments of the invention are described in detail below. Itis noted, however, that the embodiments described below do not undulylimit the contents of the invention set forth in the scope of patentclaims. Also, not all of the compositions described in the embodimentswould necessarily be essential for the solution provided by theinvention. Furthermore, the same components will be appended with thesame reference numbers, and their description will not be repeated.

1. First Embodiment

FIGS. 1A and 1B are schematic views of an angle restriction filter 10and a spectrum sensor 1 in accordance with a first embodiment of theinvention. FIG. 1A is a plan view of the spectrum sensor 1, and FIG. 1Bis a cross-sectional view taken along lines B-B of FIG. 1A. The spectrumsensor 1 includes the angle restriction filter 10, a wavelengthrestriction filter 20, and a photodetector device 30 (see FIG. 1B). InFIG. 1A, illustration of the wavelength restriction filter 20 isomitted.

In a P type silicon substrate 3 that serves as a semiconductor substratewhere the spectrum sensor 1 is formed, an electronic circuit 40 isformed for applying a predetermined reverse bias voltage to thephotodetector device 30, detecting a current based on photovoltaic powergenerated at the photodetector device 30, amplifying an analog signalaccording to the magnitude of the current, converting the analog signalto a digital signal and the like (see FIG. 1A). A plurality of aluminum(Al) alloy layers for wiring (not shown) are connected to semiconductorelements composing the electronic circuit 40, thereby providingelectrical connections among the semiconductor elements composing theelectronic circuit 40, and electrical connections between the electroniccircuit 40 and external components.

Conductive plugs (not shown) are connected between the plurality ofaluminum alloy layers. The conductive plugs electrically connectadjacent upper and lower ones of the aluminum alloy layers at placeswhere the conductive plugs are provided.

1-1. Angle Restriction Filter

As shown in FIG. 1B, the angle restriction filter 10 is formed on the Ptype silicon substrate 3 in which the photodetector device 30 is formed.In the angle restriction filter 10 of the present embodiment, an opticalpath wall section is formed by light shield members 13 composed ofconductive plugs that are formed by the same process used for theconductive plugs on the above-described electronic circuit 40. The lightshield members 13 are formed from tungsten (W) but may be formed from amaterial other than tungsten. For example, the light shield members 13may be formed from a material having a reflectance of light withwavelengths to be received by the photodetector device 30 lower than thereflectance of aluminum, such as, for example, copper, titanium nitride,titanium-tungsten, titanium, tantalum, tantalum nitride, chrome ormolybdenum.

Also, the P type silicon substrate 3 is provided thereon with aluminumalloy layers 11 as a plurality of metal layers formed by the samemultilayer wiring process used for the aluminum alloy layers on theelectronic circuit 40, which are laminated through silicon oxide (SiO₂)layers 12 serving as insulation layers each having light transmissivity(in other words, light transmissivity to light having wavelengths to bereceived by the photodetector device 30, which similarly applies to thedescription below). The embodiment is not limited to the aluminum alloylayers, and the plurality of layers 11 may be composed of copper (Cu)alloy layers.

The light shield members 13 are composed of a material that does notsubstantially transmit light with wavelengths to be received by thephotodetector device 30, and may be continuously formed in a pluralityof layers in a predetermined pattern, for example, a latticeconfiguration on the P type silicon substrate 3, such that an opticalpath in the lamination direction of the light shield members 13 isformed.

Incident angles of light that pass through the optical path arerestricted by the optical path wall sections formed with the lightshield members 13. More specifically, when light incident upon theoptical path is inclined more than a predetermined restriction angle θ(see FIG. 1B) with respect to the direction of the optical path, thelight hits the light shield members 13, whereby a portion of the lightis absorbed by the light shield members 13, and the remaining portion isreflected. The reflection is repeated until the light passes through theoptical path, whereby the reflected light becomes weaker. Therefore,light that can pass through the angle restriction filter 10 isrestricted, substantially, to light having incident angles with respectto the optical path being less than the predetermined restriction angleθ.

Areas surrounded by the light shield members 13 are composed of theabove-described silicon oxide layer 12 having light transmissivity, andthus function as light transmission sections that transmit incidentlight.

In the embodiment described above, the light shield members 13 areformed in multiple layers in a predetermined lattice pattern on the Ptype silicon substrate 3, thereby forming the optical path wallsections. Therefore, very fine patterns can be formed, and the anglerestriction filters 10 can be manufactured in a small size. Further,compared to a spectrum sensor that is formed by bonding memberstogether, the manufacturing process can be simplified, and a reductionin transmission light by adhesive can be suppressed.

In accordance with a preferred embodiment, the light shield members 13are formed from the same material (tungsten, or the like) as that of theconductive plugs described above. By this, the angle restriction filter10 can be formed by the semiconductor process at the same time when thealuminum alloy layers for wirings for the electronic circuit 40 and theconductive plugs are formed on the same P type silicon substrate 3.

In accordance with a preferred embodiment, the aluminum alloy layers 11may be formed in a region outside the optical path surrounded by thelight shield members 13 and the optical path wall sections formed withthe light shield members. In accordance with a more preferredembodiment, the optical path wall surface may be formed only from thelight shield members 13, not from the aluminum alloy layers 11 having ahigh light reflectance. As a result, it is possible to suppressincidence of light reflected from the aluminum alloy layers 11 having ahigh light reflectance in the optical path, and therefore it is possibleto make it harder for light with incident angles exceeding therestriction angle range to pass through the optical path.

Furthermore, in accordance with another preferred embodiment, the wallsurface of the optical path surrounded by the light shield members 13 isinclined with respect to a direction perpendicular to the P type siliconsubstrate 3. More specifically, the light shield member 13 in each ofthe layers has a cross-sectional shape wider toward its upper side (onthe side of the wavelength restriction filter 20), such that the wallsurface of the light shield member 13 is oriented slightly downward. Dueto the inclined wall surface of the optical path, when light that hasentered the optical path of the angle restriction filter 10 hits thewall surface of the optical path, its reflection direction becomes morecomplex. Accordingly, reflections of incident light within the opticalpath are repeated many times until the incident light has passed throughthe optical path, whereby the reflected light becomes weaker. Therefore,it is possible to make it harder for light having incident anglesexceeding the restriction angle range to pass through the optical path.

In accordance with a preferred embodiment, a titanium nitride (TiN) film14 that serves as an adhesive layer between tungsten and silicon oxideis formed on the surface of each of the light shield members 13.However, without any limitation to the aforementioned material, each ofthe light shield members 13 may be provided on its surface with a lowreflection film formed from a material having a reflectance of lightwith wavelengths to be received by the photodetector device 30 lowerthan that of aluminum, for example, titanium nitride, tungsten, copper,titanium-tungsten, titanium, tantalum, tantalum nitride, chrome ormolybdenum.

Also, in accordance with another preferred embodiment, the light shieldmembers 13 are electrically connected to the aluminum alloy layers 11through side surfaces of the aluminum alloy layers 11. As fourthsemiconductor regions 34 (to be described below) to be formed on the Ptype silicon substrate 3 are electrically connected to the bottom endsof the light shield members 13, electrical connection between thephotodiode device 30 and the aluminum alloy layers 11 can be achieved.

1-2. Wavelength Restriction Filter

The wavelength restriction filter 20 is formed on the angle restrictionfilter 10, and is composed of a plurality of laminated layers of thinfilms of a low refractive index 21 such as silicon oxide (SiO₂) and thinfilms of a high refractive index 22 such as titanium oxide (TiO₂), whichare slightly tilted with respect to the P type silicon substrate 3. Thethin films of a low refractive index 21 and the thin films of a highrefractive index 22 each having a predetermined film thickness on theorder of, for example, submicron, are laminated, for example, in about60 layers in total, thereby forming, for example, a thickness of about 6μm on the whole.

Tilt angles θ₁ and θ₂ of the low refractive index thin films 21 and thehigh refractive index thin films 22 with respect to the P type siliconsubstrate 3, may be set at, for example, 0 degree or greater but 30degrees or smaller, according to set wavelengths of light to be receivedby the photodetector device 30.

In order to have the low refractive index thin films 21 and the highrefractive index thin films 22 tilted with respect to the P type siliconsubstrate 3, for example, a tilt structure 23 having transmissivity isformed on the angle restriction filter 10, and the low refractive indexthin films 21 and the high refractive index thin films 22 are formed onthe tilt structure 23. The tilt structure 23 may be formed by, forexample, depositing a silicon oxide layer on the angle restrictionfilter 10 and processing the silicon oxide layer by a CMP (chemicalmechanical polishing) method.

In this manner, by forming in advance the tilt structures 23 having thetilt angles θ₁ and θ₂ that are different depending on the setwavelengths of light to be received by the photodetector device 30, thelow refractive index thin films 21 and the high refractive index thinfilms 22 can be formed each in the same thickness by a common process,without regard to the set wavelengths of light to be received by thephotodetector device 30.

The wavelength restriction filter 20 having such a structure describedabove restricts wavelengths of light (light that can pass through theangle restriction filter 10) incident on the angle restriction filter 10within the predetermined range of restricting angles. More specifically,a portion of incident light that has entered the wavelength restrictionfilter 20 becomes reflected light and another portion thereof becomestransmitting light at an interface between a set of the low refractiveindex thin film 21 and the high refractive index thin film 22. Then, aportion of the reflected light reflects again at an interface betweenanother set of the low refractive index thin film 21 and the highrefractive index thin film 22, and couples with the aforementionedtransmitting light. In this instance, when light has a wavelength thatmatches with the optical path length of reflected light, the reflectedlight and the transmitting light match in phase with each other, andthus strengthen each other. When light has a wavelength that does notmatch with the optical path length of reflected light, the reflectedlight and the transmitting light do not match in phase with each other,and thus weaken each other (destructively interfere with each other).

The optical path length of reflected light is determined by the tiltangles of the low refractive index thin film 21 and the high refractiveindex thin film 22 with respect to the direction of the incident light.Accordingly, when the interference action described above is repeated inthe low refractive index thin films 21 and the high refractive indexthin films 22, which amount to the total of sixty layers, light havingonly specific wavelengths can pass through the wavelength restrictionfilter 20, according to the incident angle of incident light, and areemitted from the wavelength restriction filter 20 at a predeterminedemission angle (for example, at the same angle as the incident angle tothe wavelength restriction filter 20).

The angle restriction filter 10 allows only light incident on the anglerestriction filter 10 in the predetermined range of restriction anglesto pass therein. Accordingly, the wavelengths of light that passesthrough the wavelength restriction filter 20 and the angle restrictionfilter 10 are restricted to a predetermined range of wavelengths whichis determined by the tilt angles θ₁ and θ₂ of the low refractive indexthin films 21 and the high refractive index thin films 22 with respectto the P type silicon substrate 3, and the range of restriction anglesof incident light allowed to pass by the angle restriction filter 10.

1-3. Photodetector Device

The photodetector device 30 is an element that receives light that haspassed through the wavelength restriction filter 20 and the anglerestriction filter 10, and converts the light to photovoltaic power.

The photodetector device 30 includes various kinds of semiconductorregions that are formed in the P type silicon substrate 3 by ionimplantation or the like. The semiconductor regions formed in the P typesilicon substrate 3 include, for example, a first semiconductor region31 of a first conductivity type; a second semiconductor region 32 of asecond conductivity type formed on the first semiconductor region 31; athird semiconductor region 33 of the first conductivity type formed onthe second semiconductor region 32; and a fourth semiconductor region 34of the second conductivity type formed on the second semiconductorregion 32, being surrounded by the third semiconductor region 33, andincluding an impurity having a higher concentration than that of thesecond semiconductor region 32. In this embodiment, the firstconductivity type is, for example, N type, and the second conductivitytype is, for example, P type.

The first semiconductor region 31 is electrically connected to the thirdsemiconductor region 33 through a fifth semiconductor region 35 of thefirst conductivity type. The first semiconductor region 31 is connectedto a first external electrode (not shown) through the fifthsemiconductor region 35. The fourth semiconductor region 34 is connectedto a bottom end of the angle restriction filter 10, and the anglerestriction filter 10 is further connected to a second externalelectrode (not shown). A reverse bias voltage can be applied to the PNjunction formed between the first semiconductor region 31 and the secondsemiconductor region 32 through the first external electrode and thesecond external electrode.

In the embodiment described above, the fourth semiconductor region 34 iselectrically connected to the second external electrode through theangle restriction filter 10 such that it is not necessary to provideconductive members for wiring other than the angle restriction filter 10on the photodetector device 30, and therefore a reduction in the amountof receiving light by such wirings can be avoided.

As light that has passed through the angle restriction filter 10 isreceived by the photodetector device 30, photovoltaic power is generatedat the PN junction formed between the first semiconductor region 31 andthe second semiconductor region 32, whereby an electrical current isgenerated. By detecting the electrical current by an electronic circuitconnected to the first external electrode or the second externalelectrode, the light received by the photodetector device 30 can bedetected.

It is noted that FIGS. 1A and 1B show a first photodetector device 30that receives light with wavelengths determined by the tilt angle θ₁ ofthe wavelength restriction filter 20, and a second photodetector device30 that receives light with wavelengths determined by the tilt angle θ₂.In FIG. 1B, the angle restriction filter 10 connected to the fourthsemiconductor region 34 of the first photodetector device 30 and theangle restriction filter 10 connected to the fourth semiconductor region34 of the second photodetector device 30 are connected to each other bythe aluminum alloy layers 11. Without any limitation to this structure,the angle restriction filters 10 that are independently connected to therespective photodetector devices 30 may not be mutually connected, andindependent signals of received light may be made to be detectedindependently from the respective independent photodetector devices 30.

1-4. Manufacturing Method in accordance with First Embodiment

Here, a method for manufacturing the spectrum sensor 1 in accordancewith the first embodiment will be briefly described. The spectrum sensor1 is manufactured through initially forming the photodetector device 30on the P type silicon substrate 3, then forming the angle restrictionfilter 10 on the photodetector device 30, and then forming thewavelength restriction filter 20 on the angle restriction filter 10.

First, the photodetector device 30 is formed on the P type siliconsubstrate 3. For example, at first, a first semiconductor region 31 of Ntype is formed by ion injection or the like in the P type siliconsubstrate 3. Then, a fifth semiconductor region 35 of N type and asecond semiconductor region 32 of P type are formed by ion injection orthe like applied to the first semiconductor region 31. Then, a fourthsemiconductor region 34 of P type and a third semiconductor region 33 ofN type are formed by further conducting ion injection or the likeapplied to the second semiconductor region 32. The above-described stepsmay be conducted concurrently with formation of the electronic circuit40 on the same P type silicon substrate 3.

Next, the angle restriction filter 10 is formed on the photodetectordevice 30. FIGS. 2A-2E are views showing the steps of forming the anglerestriction filter.

(1) First, a silicon oxide layer 12 of the first layer is formed withsilicon oxide or the like on the P type silicon substrate 3 where thephotodetector device 30 is formed (FIG. 2A).

(2) Then, grooves are formed in the silicon oxide layer 12 by etching aportion of the silicon oxide layer 12 (regions above the fourthsemiconductor regions 34) (FIG. 2B).

(3) Then, titanium (Ti) films 16 are formed on the bottom surfaces ofthe grooves formed in the silicon oxide layer 12, titanium nitride films14 are formed on the bottom surfaces and inner side surfaces of thegrooves, and further tungsten light shield members 13 in the first layerare embedded in the grooves. The light shield members 13 are formedconcurrently with formation of conductive plugs for connecting aluminumalloy layers for wiring for the electronic circuit 40 (FIG. 2C).

(4) Then, an aluminum alloy layer 11 of the first layer is formedconcurrently with formation of an aluminum alloy layer for wiring forthe electronic circuit 40 (FIG. 2D). It is preferred that a titaniumfilm and a titanium nitride film may be formed on the bottom surface andthe upper surface of the aluminum alloy layer 11, respectively.

(5) Then, a silicon oxide layer 12 of the second layer is formed on thesilicon oxide layer 12 of the first layer, the light shield member 13 ofthe first layer and the aluminum alloy layer 11 of the first layer (FIG.2E).

By repeating the steps (2)-(5) in a predetermined number of times, theangle restriction filter 10 is formed. It is noted that light shieldmembers 13 of the second layer are formed on the light shield members 13of the lower layer or on the silicon oxide layer 12 of the lower layer,not on the aluminum alloy layer 11 (see FIG. 2E). Light shield members13 of the third layer and above are formed on the light shield members13 in the lower layer, respectively, not on the aluminum alloy layer 11.

Next, the wavelength restriction filter 20 is formed on the anglerestriction filter 10 (see FIG. 1). For example, at first, a siliconoxide layer is formed on the angle restriction filter 10, and thesilicon oxide layer is processed into a tilt structure 23 having apredetermined angle by a CMP method or the like. Then, thin films of alower refractive index 21 and thin films of a higher refractive index 22are alternately laminated in multiple layers. The spectrum sensor 1 ismanufactured through the steps described above.

2. Second Embodiment

FIG. 3 is a schematic view of an angle restriction filter in accordancewith a second embodiment of the invention. FIG. 3 also shows a crosssection of a photodetector device. In the second embodiment, theinclination angle of the wall surface of the optical path surrounded bythe light shield members 13 (the inclination angle with respect to thedirection perpendicular to the P type silicon substrate 3) is greaterthan the inclination angle in the first embodiment. Such a structuremakes it harder for light having incident angles exceeding therestriction angle range to pass through the optical path.

In order to manufacture the angle restriction filter 10 having such astructure, when etching the silicon oxide layer 12 to form groovestherein in the manufacturing process described above, for example,etching with a stronger isotropic property may be conducted such thatthe inclination angle of the groove becomes greater. Other aspects aregenerally the same as those of the first embodiment.

3. Third Embodiment

FIG. 4 is a schematic view of an angle restriction filter in accordancewith a third embodiment of the invention. FIG. 4 also shows a crosssection of a photodetector device. In the third embodiment, the formedpattern of the light shield members 13 is changed at each layer (forexample, the width of grooves formed in the silicon oxide layer 12 forembedding the light shield members 13 may be changed at each layer),thereby forming concave and convex portions on the wall surface of theoptical path, which is different from the first embodiment. As theconcave and convex portions are formed on the wall surface of theoptical path, light that hits the wall surface of the optical path canbe reflected in an opposite direction with respect to the incidentdirection. As a result, light with incident angles exceeding therestriction angle range can be dispersed, so that the reflected light ismade difficult to reach the photodetector device 30. Other aspects aregenerally the same as those of the first embodiment.

4. Fourth Embodiment

FIG. 5 is a schematic view of an angle restriction filter in accordancewith a fourth embodiment of the invention. FIG. 5 also shows a crosssection of a photodetector device. In the fourth embodiment, thethickness of the titanium nitride film 14 formed around the light shieldmembers 13 is greater than the thickness of the titanium nitride film 14in the first embodiment. As a result, the reflectance of light at thewall surface of the optical path can be further reduced, such that lighthaving incident angles exceeding the restriction angle range are madeharder to pass through the optical path. Other aspects are generally thesame as those of the first embodiment.

5. Fifth Embodiment

FIG. 6 is a schematic view of an angle restriction filter in accordancewith a fifth embodiment of the invention. FIG. 6 also shows a crosssection of a photodetector device. In the fifth embodiment, thecomposition of the titanium nitride film 14 formed around the lightshield members 13 is different from the composition of the titaniumnitride film 14 in the first embodiment. For example, when the titaniumnitride film 14 is formed by a CVD (chemical vapor deposition) method,the processing time for a plasma treatment to remove impuritiesincluding carbon (C) or its compounds may be made shorter than thenormal processing time, or the plasma treatment may be omitted, wherebya titanium nitride film including impurities is intentionally formed.Alternatively, the compositions of the titanium nitride film 14 may bechanged, or the content of nitrogen (N) in the titanium nitride film 14may be lowered. Therefore, the reflectance of light at the wall surfaceof the optical path can be further reduced.

As a result, light with incident angles exceeding the restriction anglerange can be made difficult to pass through the optical path. Otheraspects are generally the same as those of the first embodiment.

6. Sixth Embodiment

FIG. 7 is a schematic view of an angle restriction filter in accordancewith a sixth embodiment of the invention. FIG. 7 also shows a crosssection of a photodetector device. In the sixth embodiment, the aluminumalloy layers 11 form a part of the wall surface of the optical path ofthe angle restriction filter 10, which differs from the firstembodiment. More specifically, the optical path wall section of theangle restriction filter 10 forms an optical path with a plurality ofaluminum alloy layers 11, and light shield members 13 formed between theplural aluminum alloy layers 11.

In order to manufacture the angle restriction filter 10 having such astructure, light shield members 13 in the second layer and above areformed on aluminum alloy layers 11, respectively. Other aspects aregenerally the same as those of the first embodiment.

In the sixth embodiment, portions of the wall surface of the opticalpath formed by the light shield members 13 are inclined with respect toa direction perpendicular to the P type silicon substrate 3.Accordingly, when light entering the optical path of the anglerestriction filter 10 reflects at the light shield members 13, itsreflection directions are made complex, and reflections are repeatedmany times until the incident light has passed through the optical path,such that the reflected light becomes weaker. Accordingly, light withincident angles exceeding the restriction angle range can be madedifficult to pass through the optical path.

The angle restriction filter in accordance with the sixth embodiment maybe combined with any one of the second through fifth embodiments, suchthat light with incident angles exceeding the restriction angle rangecan be made more difficult to reach the photodetector device 30. Theangle restriction filter in accordance with any one of the secondthrough sixth embodiments can be applied to the spectrum sensor inaccordance with the first embodiment.

What is claimed is:
 1. An angle restriction filter that allows lightincident thereon in a predetermined range of incident angles to pass,comprising: an optical path wall section formed from a plurality oflight shield members laminated in layers, thereby forming an opticalpath, wherein each light shield member has a cross-sectional shape widerat one end such that a surface forming a portion of the optical pathwall is oriented slightly downward; and a light transmission sectionformed in a region surrounded by the optical path wall section.
 2. Anangle restriction filter according to claim 1, wherein the layersinclude a common material having a reflectance lower than a reflectanceof aluminum.
 3. An angle restriction filter according to claim 1,wherein the optical path wall section and the light transmission sectionare formed on a semiconductor substrate, and a plurality of metal layersare laminated respectively through dielectric layers in a region outsidethe optical path and the optical path wall section on the semiconductorsubstrate.
 4. An angle restriction filter according to claim 3, whereinthe light shield members are formed from a conductive material, andelectrically connected to the plurality of metal layers.
 5. An anglerestriction filter according to claim 1, wherein the optical pathdefines a wall surface, the wall surface having an inclination sectionthat inclines with respect to a direction perpendicular to thesubstrate.
 6. An angle restriction filter according to claim 1, whereineach of the light shield members is provided on a surface thereof with afilm formed from a material having a reflectance lower than areflectance of aluminum.
 7. An angle restriction filter according toclaim 1, wherein the optical path defines a wall surface having concaveand convex portions formed through changing a forming pattern of each ofthe light shield members at each layer.
 8. A spectrum sensor comprising:the angle restriction filter recited in claim 1; a wavelengthrestriction filter that restricts wavelengths of light that passesthrough the angle restriction filter; and a photodetector device thatdetects light that has passed through the angle restriction filter andthe wavelength restriction filter.
 9. An angle restriction filter thatrestricts incident angles of light that passes through an optical path,comprising: an optical path wall section formed from a plurality oflight shield members laminated in layers, thereby forming the opticalpath, wherein each light shield member has a cross-sectional shape widerat one end such that a surface forming a portion of the optical pathwall is oriented slightly downward; and a light transmission sectionformed in a region surrounded by the optical path wall section.
 10. Anangle restriction filter according to claim 9, wherein the layersinclude a common material having a reflectance lower than a reflectanceof aluminum.
 11. An angle restriction filter according to claim 9,wherein the optical path wall section and the light transmission sectionare formed on a semiconductor substrate, and a plurality of metal layersare laminated respectively through dielectric layers in a region outsidethe optical path and the optical path wall section on the semiconductorsubstrate.
 12. An angle restriction filter according to claim 11,wherein the light shield members are formed from a conductive material,and electrically connected to the plurality of metal layers.
 13. Anangle restriction filter according to claim 9, wherein the optical pathdefines a wall surface, the wall surface having an inclination sectionthat is inclined with respect to a direction perpendicular to thesubstrate.
 14. An angle restriction filter according to claim 9, whereineach of the light shield members is provided on a surface thereof with afilm formed from a material having a reflectance lower than areflectance of aluminum.
 15. An angle restriction filter according toclaim 9, wherein the optical path defines a wall surface having concaveand convex portions formed through changing a forming pattern of each ofthe light shield members at each layer.
 16. A spectrum sensorcomprising: the angle restriction filter recited in claim 9; awavelength restriction filter that restricts wavelengths of light thatpasses through the angle restriction filter; and a photodetector devicethat detects light that has passed through the angle restriction filterand the wavelength restriction filter.